The invention concerns a gas turbine engine with pulverized coal firing especially for aircraft, consisting of at least one air compressor, a combustion chamber with burners, and a gas turbine, with centrifuging of the solid combustion residues present in the combustible gas and their elimination through openings in the engine casing with the aid of a bypass flow branching off from the combustible gas.
Due to the relatively limited supply and greatly increased cost of crude oils, efforts are being made to increasingly fall back on other sources of energy.
Hydrogen would be an ideal source of energy, however, its manufacture and conversion to the liquid state ist costly and storage and transport is also difficult because of the problems of insulation. Water as a means of electricity generation which renews itself, is bound to the geographic location. The generation of electricity from atomic energy requires, at least at the present time, the construction of large power plants and necessitates highly qualified personnel for their operation.
Given these preconditions coal clearly suggests itself as a source of energy. Coal is abundantly available worldwide and easy to transport. It is known above all from its use in pure steam power plants. Experiments have already been made with pulverized coal firing in stationary gas turbine power plants, however these experiments did not lead to useful results which would have permitted industrial application.
The solid combustion residues in the combustible gas consist of unburned pulverized coal and ash and act as a kind of abrasive powder whereby the first row of turbine blades is exposed to strong erosion. The roots of the stator blades are particularly affected because of the solid particles which are thrown out due to centrifugal force.
The hot particles however stick to all surfaces coming in contact with the combustible gas, which leads to a partial clogging of the flow channels within the blading. This disadvantage has not been adequately alleviated through the addition of chemical additives.
To a certain extent this problem can be remedied by the arrangement of exit slots in the combustion chamber or gas turbine casings in order to blow out the solid residue in the combustible gas. However, in order to remove the necessary, i.e. most of the residue in the combustible gas, such a large amount of the combustible gas would have had to have been diverted for the removal of the residues that because of the high energy losses an economic operation would no longer have been possible. Thus one had to settle on a--inevitably unsatisfactory--compromise in that whilst the bypass flow from the combustible gas was kept within acceptable limits, there remained a relatively large amount of combustion residue which led to the above-mentioned erosion damage in the gas turbine blading, albeit only after a somewhat longer time span. Economic industrial operation was not possible in this manner.
Gas turbine engines with pulverized coal firing for aircraft did not proceed beyond the planning stages because of the same problems, although coal ash being a fertilizer could be widely distributed without problems by elimination through the exhaust.
The task underlying this invention was to create a gas turbine engine of the type described at the beginning which permits economic longterm operation. This problem is solved by an installation for the utilization of the energy contained in the bypass flow.
Through the provision of such an installation it is possible to remove such a large part of the solid combustion residues from the combustible gas as is necessary to avoid unduly high erosion of the gas turbine blading or even clogging of flow channels and as a result achieve long operating times. Despite the fact that a larger bypass flow is necessary than in conventional test installations through the utilization of the energy contained in the bypass flow the efficiency as a whole of the power plant is hardly affected.
The installation just mentioned is best used in aircraft in at least one thrust nozzle which is impinged upon by the bypass flow, the function of which is to augment the thrust of the main thrust nozzle of the engine: in a stationary power plant in at least one heat exchanger through which the bypass flow flows, which, for example, serves to preheat the air for combustion. In order to effect a more rapid elimination of the combustion residues through openings in the combustion chamber or gas turbine casings, it is advantageous to produce swirl of the combustible gas prior to entrance in the gas turbine blading.